From 2aa5405e323ce29c03148d4f7f7ae0e1e7471112 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Thu, 17 Sep 2009 21:49:15 +0000
Subject: [PATCH] CSV NULL Documentation

Update docs to clearly explain NULL value matching behavior, per Andrew.

Backpatch to 8.4.X.
---
 doc/src/sgml/ref/copy.sgml | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index a89f33eb5a..859b0f924d 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -550,10 +550,13 @@ COPY <replaceable class="parameter">count</replaceable>
    <para>
     The <literal>CSV</> format has no standard way to distinguish a
     <literal>NULL</> value from an empty string.
-    <productname>PostgreSQL</>'s <command>COPY</> handles this using
-    quoting. A <literal>NULL</> is output as an empty string without
-    quotes, while an empty string data value is double-quoted
-    (<literal>""</>).  Reading values follows similar rules. You can
+    <productname>PostgreSQL</>'s <command>COPY</> handles this by
+    quoting. A <literal>NULL</> is output as the <literal>NULL</>
+    parameter and is not quoted, while a non-NULL value matching the
+    the <literal>NULL</> parameter string is quoted. Therefore, using the default
+    settings, a <literal>NULL</> is written as an unquoted empty
+    string, while an empty string data value is written with double quotes
+    (<literal>""</>). Reading values follows similar rules. You can
     use <literal>FORCE NOT NULL</> to prevent <literal>NULL</> input
     comparisons for specific columns.
    </para>
-- 
2.39.5